Penetrating ray emission coding



Oct. 18, 1960 R. @.EDHOLM. PENETRATING RAY EMIssIoN comme Filed Dec. 27. 1957 /NvEn/Ton RoLF 6. EDHOLM ema/w ATT RNEys llniteri tates lul PENE'IRATWG RAY Eli/HSSEGN CDENG Rolf G. Edholm, Milwaukee, Wis., assigner to General Electric Company, a corporation of New York Fried nec. 27, 1957, ser. No. 705,652

claims. (ci. 25e-5s) This invention relates to article classification, and particularly to a method and apparatus employing the emission and diffraction characteristics of penetrating rays for decoding article carrying indicia.

Major objects are to provide:

(a) An improved method of coding and decoding particularly adapted for use in the classification of a plurality of different articles as in manufacturing plants or warehouses, advantageously utilizing known characteristics of certain penetrating radiation, such as X-rays or gamma rays, including emission or secondary radiation and diffraction.

(b) An improved method and apparatus for high-speed decoding which is insensitive to exposure by light within the visible spectrum and equally insensitive to -local magnetic disturbances either of which may affect the dependability of existing decoding systems.

(c) A coding and decoding system permitting use of a coding tape or label of rugged construction, the effectiveness of which cannot be destroyed by fading due to light exposure; which does not employ radioactive materials; is easily applied to a carton or directly to an article; is able to withstand rough handling of the article to which this is applied; and which will withstand exposure to the elements for long periods of time.

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the provision of an improved method of coding and decoding by use of penetrating rays, and to the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth, and the scope of the application of which will be indicated in the appended claims.

Substantial advances, particularly during the past decade, in the article and material handling fields coupled with automated manufacturing and processing have dictated a need for parallel improvements in the field of coding and `decoding as applied to article classification. Considerable attention, therefore, has been directed toward improving such methods and apparatus in view of speed and dependability limitations imposed on mechanical and other coding systems heretofore employed. Optical-electrical as well as magnetic and other principles are incorporated in recently developed systems, with wide use being made of photo-responsive devices and magnetic tape and the like for optical and magnetic scanning, respectively. Coding techniques have been suggested for presentation of both black and white and color `codes in a plurality of forms for decoding by light beam scanning in a manner to provide electrical signals indicative of various classification code patterns.

It is known to use one or more radiation detection devices for sorting radioactive materials, and during recent years proposals have been advanced for use of radioactive materials, such as isotopes, for production of code signals to be decoded by such detectors. The dangers Patentes ont., is, raso jice -attendant such systems are apparent. Use of X-rays is known in connection with grading or classifying objects by detecting the opacity thereof, and classification systems have been worked out on that principle. Such a system effects classification and sorting by comparing signals derived from the X-ray opacity pattern with a reference signal from objects of known characteristics, and automatic handling and sorting mechanism may be associated therewith for sorting like from funlike objects.

Penetrating rays, such as gamma and beta rays, are commonly employed in the gauging field; for example, for the purpose of gauging thickness or -width of moving metal such as in steel mills and in coating thickness gauges which may employ the principle of back scatter, secondary radiation, or diffraction. The subject of gauging is mentioned since the boundary line between gauging and article classification is often a thin one. This is particularly true when the object itself serves as the indicia lfrom which a read-out signal is produced. It -does not follow, however, that this type of classification involves either coding or decoding, since the object carries no code indicia as such.

The principles governing the behavior of penetrating rays are well known, hence a cursory treatment will sulce to explain 4the present invention and its adaptation to apparatus shown and described herein. While the following remarks will be directed to X-rays, other penetrating rays such as gamma rays outside the X-ray spectrum, or beta rays, as from an isotope source, for example, may be employed in the place of X-rays. Since the embodiment of the present invention employs both the principles of X-ray emission and diffraction (including X-ray spectrometry), the following remarks relative to each phenomenon may aid in an understanding of those principles.

X-rays as produced in an ordinary X-ray tube are of various wave lengths and intensities, and differ in these characteristics based on the `degree of tube vacuum, the target material and the generating potential between target and cathode. Such rays, generated by high energy electron impingement on target material in a vacuum may be used for irradiation `of elements, particularly the metals, to excite those elements to produce emitted or secondary X-rays which with a vfew exceptions are identical with but lower in intensity than the X-radiation produced when the same element is used as the target in an X-ray tube. The production of such rays is variously termed emission, secondary radiation and fluorescense, but will herein be termed emission Each element thus excited has a characteristic radiation by which the element can be `identified by known means of detection.

X-rays are diffractable by crystals and that principle is employed in the known X-ray diffraction and spectroscopic techniques. When a monochromatic X-ray beam is reflected by a cleavage face (or by any other atomic plane) of a crystal, according to` the ordinary laws of optical reflection, Le., the incident and reflected beams are in the same plane (perpendicular to the reflecting face) and the angles between those two beams and the reflecting face are equal. In addition to those laws, the following condition must be fulfilled if reflection is to occur:

n r=2d sin q (Braggs Law) where )t is the wave length of the monochromatic radiathe beam and the plane, and n indicates the order of the reflection. It follows that different monochromatic rays from a source of polychromatic X-rays will be reflected by a crystal at diiferent angles, hence by limitation of the effective operating angles between source, crystal and ray detector, it is possible to select for detection only such rays as have reflection characteristics to fall between those angles.

The phenomena of emission is accompanied by some diffraction, just fas diffraction is accompanied by some emission. When the purpose is to identify elements by diffraction techniques, such emission is undesirable since it is of random angular distribution and may interfere with or mask the diifracted rays, hence it is common practice to employ X-ray wave lengths and techniques which minimize such emission. Since the present invention utilizes the emission principle as the first step in decoding, `a reverse procedure is employed with X-ray Wave lengths selected to promote emission and minimize diffraction of an X-ray beam directed to a code member as hereinafter described.

In the drawings:

Fig. l shows apparatus, shown partially in plan and partially in diagram form, incorporating the invention.

Fig. 2 is a plan view of a coded tape member showing a code coniiguration of like metal particles.

Fig. 3 is a plan view of a coded tape showing random distribution of particles of different metals mixed in predetermined percentages.

Fig. 4 is a fragmentary vertical section of a coding tape, greatly enlarged, showing layers of metal particles between plastic layers.

Fig. 5 is a view, similar to Fig. 4, but showing a coding tape comprised of short strips of thin metallic sheet stock of different metals disposed in layers.

Fig. l shows a plurality of spaced articles 1li continuously moved by a belt-type conveyor 11 driven by a motor 12 to move articles 11i from a loading station adjacent a guide roller 13 in the arrow direction to a removal station 14 adjacent power roller 1S, driven by motor 12 through drive shaft 16. Each article has affixed thereto, preferably in the same relative position with lrespect to the conveyor, but at least at the same vertical height above the base of the article which rests on the conveyor, a coded member or tape 18 containing a plurality of different metals or a single metal in pattern form or varying quantities of the same metal as hereinafter described. Code members 18 are positioned to be drawn by conveyor 1i into an X-ray beam 2@ generated by X-ray tube 21. Tube 21 may be of conventional construction, including in envelope 22., a cathode 23 of the hot lament type connected to an excitation source 24, and an anode or target 25, maintained at high positive potential by a voltage source 26. The characteristics of tube 21, such as the Vdegree of evacuation, the composition of target 25 and the potential of source 26, as well as the angle at which beam 20 hits the coded label 18 are selected in a manner well known in the art to produce maximum emission and minimum diraction as label 18 containing metallic particles is brought into beam 20.

As stated above, emitted rays are of random angulation, hence wide scattering results, but with suitable shielding, not shown, provided with a beam forming slit, a sample beam 28 of emitted or secondarily radiated rays is selected and directed as shown to a diifraction crystal or crystal grating 30. The resulting sample beam will, however, contain all types of rays emitted by the code label due to the random nature of emission, and by proper selection of the coded metals in View of the characteristics of X-ray tube 21, the angulation of beam 28 may be such as to exclude all dilfracted rays resulting from the passage of code label 18 through the primary beam 20. Assuming code member 18 to comprise a plurality of vvdiiferent metals, beam Zwill be polychromatic, containing the characteristic radiations Vof the different metals of the code label, but since dilracted rays are suppressed,

the rays directed to crystal 3@ are independent of those comprising beam Ztl, and for practical purposes are the same as would have been generated by an X-ray tube target made up of the various metals contained in code label 18.

To avoid repetition, and also complicating the drawing, only one crystal 30 has been shown diracting or reflecting characteristic radiation of one particular wave length out of polychromatic beam 23 and directing it as monochromatic radiation 32 of various orders of diffraction to detector 33. But characteristic radiations of diverse wave lengths from other elements present in the code strip 18 also appear in beam 2S, which radiations are not projected into the one detector under consideration. In fact, beam 28 is only one of a group of such beams of polychromatic charactistic radiation and other beams are available for being directed to other crystals 30 that lare oriented to primarily dilfract characteristic radiation of wave length corresponding with another metal that is present in code strip 13. By this means, other detectors that are adjusted to intercept other diifracted characteristic rays initiate a response in the discriminator that results in sorting out items 1t) according to the metals present in the code strips they bear.

When a code strip having a single metal is used, the type in Fig. 2 for example, the detector may be adjusted to respond according to the intensity of the characteristic radiation, corresponding with the amount of that metal which is present in successive strips, rather than to different wave lengths, in which case only one crystal 30 and one beam 28 are used. Where characteristic radiation intensity variations between different codes strips is relied upon, rather than differences in wave lengths, to stimulate the detector 33, it is not necessary to direct the radiation with a crystal such as 34) and that element may be eliminated. Of course, it will still be necessary to use plural detectors, each of which responds to a diiferent level of radiation in order to distinguish the code information conveyed by the strips. ln this case, detector 33 may be any of the devices well known to those practicing in the radiation arts, such as proportional counters or pulse amplitude responsive devices.

There is a high limit on the number of possible codes resulting from permutations of various types of metal particles taken in conjunction with various levels of those metals present as will be evident from a later discussion of the Various code strips disclosed by Figs. 2-5.

Crystal 30 reects the dilferent monochromatic rays which constitute beam 2S at different angles to form a dilracted beam in accordance with Braggs law, above, the reflected rays 32 being intercepted by detector 33, which may be of the ion chamber or Geiger-Muller type. It is readily seen that crystal 30 and detector 33 servo as `an X-ray spectrometer to separate and detect the diiferent monochromatic rays emitted by code label 18, and in this manner, a coded indicia, as described in more detail below, in the form of diiferent kinds of metal, or 'varying proportions or thicknesses of metals, or both, may be decoded by detector 33 ina manner well known in the art of X-ray spectrometry. Since code label 18 will normally move past beam 2t) at conveyor speed, and it would be undesirable to stop the conveyor for decoding, it will be necessary to discriminate between spurious signals, resulting from incomplete framing of the code label in the beam, andthe signal resulting from complete framing, hence detector 33 has incorporated therein or associated therewith ya suitable known type of discriminator circuit for that purpose. The detector output signals may be employed to eiect a plurality of operations, such as the control `of article transfer conveyors, or for counting and computing the types and numbers of a Variety of yarticles passing the decoding station, as illustrated by the counter 52' and computer 53 as shown.

Both the composition and configuration of coding label 18 may be subject to wide variation. While a code pattern made up of several different metals in iixed percentages, as shown at 34 in Fig. 3, is preferred, particles of the same metal in varying quantities in diierent identifying strips, as shown by like metallic particles 35, Fig. 2, may be used, but the number of possible indicia would be more limited than by use of different metals. A very satisfactory tape-like code label may be produced by deposition of one or more layers of a mixture of particles of several metals on a plastic base -by known evaporation processes. Fig. 4 illustrates a multiple layer label formed in this manner on a base tape 36 upon which metal containing layers 37, 38 and 39 are bonded in geometric configuration or otherwise to base 36 and between plastic layers 40 and 41. Like metal particles may be applied to form each layer 37, 38 and 39 with diierent metals used for each layer. Code label fabrication is not necessarily limited to the use of metallic particles, and Fig. 5 shows an alternate construction in which layers 43, 44 and 45 of narrow metal strips are disposed transverse to the long dimension of the label and bonded between plastic layers 46, 47, 48 and 49, the strips of each layer being of a diierent metal. As is evident from the nature of X-rays either a two or three dimensional pattern configuration is optional at the thicknesses involved. The pattern should be such as to present only the full level decoded signal desired when fully framed in the beam, the detection of which can readily be accomplished by discriminator and detector apparatus currently available for X-ray diiraction and X-ray spectroscopic use.

What I claim is:

1. The method of identifying successive articles by coding and decoding comprising the steps of applying code members of a plurality of metal particles in intelligence conveying configuration on the articles, subjecting said successive members to exciting rays to cause said particles to emit secondary rays characteristic of the coded metallic content of said members, and detecting said emitted rays to produce an output signal indicative of the intelligence thus decoded from said metallic particle content of said member.

2. 'Ihe method of identifying successive articles comprising subjecting different code members adapted to be attached to different articles to be identified and containing a predetermined plurality of different metals to a source of exciting radiation to produce secondarily emitted rays characteristic of the metals so irradiated, and detecting said characteristic rays to produce an output signal indicative of the indicia conveyed by said metals.

3. A method of identifying successive -articles by coding and decoding comprising the steps of forming different members containing a predetermined plurality of diierent metals by non-metallic material and carrying the members on the articles, subjecting said members to a beam of X-rays to produce polychromatic secondary radiation indicative of the dilerent metals, subjecting said polychromatic radiation to a dispersive sys- Item adapted to resolve identifying secondary radiation, and detecting said separated rays to produce a read-out signal indicative of the code characteristics of said metals.

4. The method of article identification consisting of providing code members containing a diierent predetermined metallic aggregate on different articles, attaching said members to articles, subjecting said members successively to X-radiation in a manner to excite secondary X- ray emission by the metal of said member, diiracting said emitted X-rays and detecting the diffracted X-rays to produce an output signal indicative of the code represented by said metallic aggregate.

5. In apparatus of the type in which a plurality of code carrying articles are conveyed past a decoding station for identiication, a source of primary X-rays positioned at said station and beamed toward the path of article conveyance, a code member adapted for attachment to an article in position to pass through said X-rays and comprising plural metallic elements held by nonmetallic means, at least one crystal element positioned in the path of X-rays secondarily emitted by the metals irradiated by said primary X-rays for the diffraction thereof, and an X-ray detector positioned to receive rays diffracted by said crystal element for conversion of said diffracted secondarily emitted X-rays to `an electric signal representative of the coded indicia carried by said me-` tallic elements.

6. lln a device of the type .in which a plurality of articles to be classified by decoding pass a fixed point, said articles being adapted to have xed thereto an identifying code label in a position to pass said point for decoding; a primary source of X-rays positioned at said point and beamed toward the path through which said articles pass, said code label containing a plurality of diierent metals held by a non-metallic bond and positioned to be scanned by X-rays from said primary source as its article passes said point to eiect emission of characteristic secondary X-rays from said metals, at least one crystal positioned to receive said emitted X-rays for the diffraction thereof, and X-ray sensitive detector means positioned within the path of said diffracted X-rays for producing an electrical signal indicative of the crystalline characteristics of the metallic content of said code member.

7. In apparatus for article identification, the combination with a decoding station and conveyorrmeans for moving articles past said station; of a code label adapted for attachment to an article in a position to move past said station, said label containing a plurality of metal particles held by a non-metallic material, a source of X- radiation beamed toward said conveyor in a position to be intercepted by said code label to produce secondarily emitted X-rays characteristic of the metals in said label, at least one crystal positioned to receive said emitted X-rays for separation in accordance With the diffraction indices thereof, and means for `detecting said difracted rays by measuring the ionizing effect thereof to produce a signal indicative of the presence of various metallic particles in the label.

8. As an article of manufacture, a code member adapted to be subjected to X-rays, said member comprising a plurality of diierent metals disposed in a coded configuration and maintained bonded by a non-metallic form sustaining material.

9. As an article of manufacture, a code member adapted to be subjected to and excited by X-rays to emit characteristic radiation, said member comprising an aggregate of predetermined quantities of different metals, and non-metallic means holding said metals in fixed position with respect to each other.

10. As an article of manufacture, a code member yadapted to be subjected to and excited by X-rays to emit characteristic radiation, said member comprising a predetermined quantity of a metal, and non-metallic binding means holding said metal.

References Cited in the file of this patent UNITED STATES PATENTS 2,162,420 Buckley .lune 13, 1939 2,179,859 Page Nov. 14, 1939 2,456,816 Daly Dec. 2l, 1948 2,783,385 Wytzes Feb. 26, 1957 

